Fish need dissolved oxygen in the water to survive because they breathe through their gills, which extract oxygen from the water to transport it into their bodies and allow cellular respiration.
Just like us, fish need oxygen to function. But unlike us, they extract this oxygen directly from the water through their gills. The dissolved oxygen present in the water passes through the very thin membrane of the gills, enters the fish's blood, and then circulates to its organs. This oxygen allows the organs and cells to produce the energy needed for swimming, digestion, and reproduction. Without a sufficient amount of dissolved oxygen, fish quickly struggle, and their survival is directly threatened.
Fish absorb dissolved oxygen through their gills, which are highly vascularized filters located beneath their opercula. Water enters through the fish's mouth, passes over the gills where a gas exchange occurs: oxygen moves from the water into the blood, and carbon dioxide takes the opposite route to be expelled. This process is greatly facilitated by the very thin and richly supplied structure of the gill filaments, which significantly increase the exchange surface area. It is efficient and natural: somewhat like our lungs, but specially adapted for life underwater.
If the water lacks dissolved oxygen, fish really struggle. Their breathing becomes more rapid, they often rise to the surface in search of air (a clear sign that they're suffocating a bit), and their bodies become completely stressed. In the long term, they risk serious internal damage such as reduced growth or reproductive problems. In the worst-case scenario, prolonged absence of oxygen leads directly to certain death, sometimes causing massive die-offs in lakes or rivers. This phenomenon, often referred to as hypoxia, can truly devastate an entire aquatic ecosystem if nothing is quickly done to restore balance.
Faced with oxygen-poor waters, fish develop adaptations that are as ingenious as they are surprising. Some species, like catfish, adopt an original strategy: they breathe air at the surface using special organs, somewhat like our lungs, but simpler! Others, including carp and goldfish, manage to slow down their metabolism, thereby reducing their oxygen needs—just as clever as built-in energy saving. We even see some fish capable of expanding the surface area of their gills to better capture the little available oxygen: a sort of superpower for surviving in extreme conditions.
Goldfish, contrary to popular belief, quickly suffer from a lack of oxygen when kept in a round bowl without an aeration system. Rectangular aquariums equipped with air pumps or filters are better suited to their needs.
The common carp has an incredible ability to withstand very low oxygen levels. It possesses unique mechanisms that allow it to temporarily convert sugars into alcohol to survive for long periods in anaerobic conditions!
The quality monitoring of aquaculture farms systematically includes close monitoring of dissolved oxygen levels in the water. This helps to prevent massive fish losses due to occasional episodes of hypoxia (lack of oxygen).
The colder the water, the more dissolved oxygen it can hold: this is why fish living in warm waters are often more sensitive to episodes of oxygen deficiency.
No, different species of fish have varying requirements or tolerances for dissolved oxygen. For example, catfish or goldfish can adapt to low concentrations of oxygen, while trout require relatively high levels of dissolved oxygen.
You can increase dissolved oxygen by agitating the water more, for example, with a pump or a filter that creates ripples on the surface, by limiting the water temperature, or by introducing live aquatic plants.
Sure! Here’s the translation: "Yes, aquatic plants generate oxygen during the day through photosynthesis. However, at night, they consume oxygen, which can temporarily reduce the level of dissolved oxygen in the water."
When a pond lacks sufficient dissolved oxygen, fish are forced to rise to the surface to capture the oxygen present at the air-water interface, a phenomenon known as 'piping'. This situation often indicates an ecological imbalance or overpopulation in the pond.
Yes, generally cold water contains more dissolved oxygen than warm water. The colder the water, the more it can absorb and retain large amounts of oxygen, which is essential for the survival of fish that breathe through their gills.
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